Welcome to HCM,
Situps can cause abdominal pain
especially on the sides of abdomen but very rarely in mid-lower abs.About those loud bubbling sounds,it just makes sense to mention that these are just intestinal sounds, but they are usually not so audible as your boyfriend seems to claim,but if it is so then may be you got to ask him how has been his bowel habits recently,very constipated or too much vigorous so as to cause diarrhea
He can just eat himself examined by his Primary care
physician who can assess him clinically and then advise accordingly.
Hope your queries have been answered well.
Have a healthy life.